1. Field of the Invention
The present invention relates to an apparatus for verifying pattern data used in a step-and-repeat process for producing the same patterns, based on the pattern data, regularly arranged on a substance, and particularly, to an apparatus for verifying chip pattern data used in a step-and-repeat process for producing the same chip patterns regularly arranged on a substance to be a photomask used for fabricating integrated circuit devices.
2. Description of the Related Art
Integrated circuit (IC) devices are usually fabricated by using a plurality of photomasks. Since the IC device becomes very minute as seen in a Large Scale Integration circuit (LSI) device or a Very Large Scale Integration circuit (VLSI) device, a large number of photomasks fabricated with very high accuracy are used in a manner of superimposing for patterning very minute circuits of the IC devices. Furthermore, recently, the life of IC products has become very short, so that new IC devices, and accordingly, new photomasks for the new IC devices have to be always designed and fabricated. Therefore, it becomes very important to raise the yield rate and shorten the expended time of the photomasks for reducing the production costs and expediting the issuing date of the new products of the IC devices.
A photomask pattern has been fabricated through a step-and-repeat process by using optically a reticle image of a chip circuit pattern (base pattern). However, recently, only the data on the chip circuit pattern are directly used in the step-and-repeat process, not the reticle optical image.
The chip circuit pattern is designed by a circuit designer, using a Computer Aided Design (CAD) system, and digital data, which will be called "chip circuit pattern data" ("base pattern data") hereinafter, of a chip circuit pattern of the IC device are made and stored in a data storing medium such as a magnetic tape. The chip circuit pattern data are combined with additional data into combined data, which will be called "chip pattern data" ("unit pattern data") (not "chip circuit pattern data") hereinafter, by a chip data combining system. The additional data will be described later. The photomask is fabricated by an apparatus, generally called a "stepper", for performing the step-and-repeat process, using the chip pattern data and "process data" required to carry out the step-and-repeat process by the stepper.
The photomask pattern includes a plurality of chip circuit patterns usually arranged orthogonally in a matrix so as to have a narrow space between chip circuit patterns adjacent each other in both X and Y directions of the matrix. The narrow space has a width of approximately 100 microns, and a wafer is cut into a plurality of divided IC chips along a center line of each space when all chip circuits for the IC devices have been formed on the wafer by using many kinds of photomasks. Generally, the cutting line in the space is called a "scribe line" and the space surrounding the chip circuit pattern is called a "scribe frame". FIG. 1 shows partially the pattern of a photomask 1. In FIG. 1, chip circuit patterns 2 are arranged in a matrix on X-Y orthogonal coordinates, having an equal space 3 between chip circuit patterns 2 adjacent each other in both X and Y directions. In this situation, scribe lines 4 are supposed to run along center lines of the narrow spaces 3 respectively as shown by thin dotted lines in FIG. 1.
The chip pattern data include information not only on the chip circuit pattern but also on a scribe frame pattern and further on at least one subsidiary pattern located in the scribe frame pattern, which is shown by a chip pattern 5 contained in a thick dotted square in FIG. 1. Thus, the chip pattern data include information for patterning the chip pattern 5 consisting of one chip circuit pattern 2, a scribe frame pattern 6 and subsidiary patterns 7. In FIG. 1, two subsidiary patterns 7 are depicted by "+" marks, because the rotation of the chip pattern can be corrected more precisely than a case of using only one subsidiary pattern.
Each subsidiary pattern 7 includes, for example, a positioning mark and a vernier pattern for inspecting whether each chip circuit pattern of one photomask is correctly projected on a wafer, compared with the chip circuit patterns due to other photomasks. That is, when more than two photomasks are used in the superimposed manner on the wafer, the position, rotation and size of each chip circuit pattern projected on the wafer by the present photomask can be inspected, compared with those having been previously formed on the wafer by other photomasks.
The additional data added to the chip circuit pattern data include information on a chip size, a width of the scribe frame, the subsidiary patterns and a kind of resist used for pattern etching.
As stated before, the chip circuit pattern data and the additional data are combined into the chip pattern data and the photomask is fabricated by applying the chip pattern data to the stepper. However, in this case, there has been a problem in regard to the subsidiary patterns. As shown in FIG. 1, since the chip pattern 5 includes the scribe frame pattern 6 so as to be commonly used with the adjacent chip patterns 5, the subsidiary patterns 7 substantially overlap each other in the step-and-repeat process. The scribe frame pattern 6 has two types, a positive type and a negative type, corresponding to the characteristics of the resist. The positive type pattern is a pattern through which a portion, corresponding to the scribe frame, of a substance of the photomask is not etched, leaving the subsidiary patterns so as to be etched. On the contrary, the negative type pattern is a pattern through which a portion, corresponding to the scribe frame, of the substance is etched, leaving the subsidiary patterns so as not to be etched. Therefore, in the case of the positive type, the substance, where the scribe frame pattern 6 of the chip pattern 5 has been exposed, can be etched by the subsidiary pattern 7 of the neighboring chip pattern 5 without paying any attention. However, in the case of the negative type, it could not be done unless the substance, where the subsidiary pattern 7 of the neighboring chip pattern 5 is supposed to be exposed, is protected from being etched by the scribe frame pattern 6 of the chip pattern 5.
FIG. 2 illustrates a chip pattern in the case of using the chip pattern data including the data on the scribe frame pattern being the negative type. In FIG. 2, the same reference number as in FIG. 1 designates the same pattern as in FIG. 1. If there were no protecting means from exposure, the subsidiary patterns 7 of the neighboring chip patterns could not be formed on the substance of the photomask in the step-and-repeat process. Therefore, portions on the substance, on which other subsidiary patterns 7 of the neighboring chip patterns are projected, from being etched by protecting patterns which will be called "margin patterns" hereinafter. In FIG. 2, solid squares 71' and 72' are the margin patterns for the subsidiary pattern 71 of the one neighboring chip pattern 5 (at the right hand side in FIG. 2) and the subsidiary pattern 72 of the other neighboring chip pattern 5 (at the left hand side) respectively. These subsidiary patterns 71 and 72 and the margin patterns 71' and 72' are depicted in dotted circles enlarged.
A lot of photomasks are required to fabricate the IC devices as stated before, and each photomask requires the chip pattern including the scribe frame pattern of either the positive or the negative type. The selection of the scribe pattern type occurs too often, so that wrong selections frequently take place, even though visual verification of the chip pattern is performed in a simulated way before the chip pattern data are stored in the magnetic tape. This is because too much complicated work of the selection and the verification are required in the fabrication of the photomasks, and this has been the problem to be solved.